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In an adiabatic compressed air energy storage process (A-CAES), heat storage tank operation is a key factor that determines the overall energy performance of the process. To highlight energy issues linked to a correct tank design in the specific case of an A-CAES system, a two-dimensional thermal numerical model was developed. Thermal efficiencies of the tank are presented with abacus defined from the four dimensionless numbers defining the thermal behavior of the reservoir. Cycling effects are explored with a realistic case study corresponding to an A-CAES system design to deliver an electrical power of 250 MWel for 4 h, the daily peak demand. Extended beyond the thermal reservoir, A-CAES thermodynamic analysis combined with the dynamic simulation makes it possible to generate a direct quantitative link between reservoir sizing and A-CAES global efficiency. [ABSTRACT FROM AUTHOR]

Recycled ceramics made of inertized asbestos containing wastes have been submitted to high pressure/temperature cycling tests in the operating range of ACAES and CSP applications. Ten successive cycles between room conditions and 610 °C/30 bars for a cumulated duration of 2500 h lead to a validation of the ability of the material to resist to those constrains. The Wollastonite/Augite initial structure is gradually transformed in a unique Augite containing material. While mechanical parameters and density are unchanged, thermal capacity is reduced by 5% and thermal conductivity increased by 30%. This last result offers an advantageous way to enhance the thermal conductivity of those recycled ceramics, a key parameter to control the charge/discharge power in TES systems. [ABSTRACT FROM AUTHOR]

Highlights: [•] Analysis of experimental data from a BTES comprising three 180m-deep boreholes. [•] Development of a 3D multilayer numerical model validated against experimental data. [•] Long-term simulations of ground temperature behaviour in several BTES configurations. [•] Theoretical relation to evaluate the storage performances of any cylindrical BTES. [ABSTRACT FROM AUTHOR]

Abstract: This work aims to evaluate the performance of a solar domestic hot water (SDHW) system including a latent storage material. The originality of our approach consists to place a composite made of compressed expanded natural graphite (CENG) and phase change material (PCM) directly inside a flat plate solar collector in order to replace the traditional copper-based solar absorber. According to this target, the study is composed of two steps: the composites preparation and characterization; and the analysis of the system to achieve optimal integration of the material in the process. The present paper is focused on the selection of the most promising composite to implement in the solar collector. In order to reach this objective, several composites based on CENG and various storage materials (paraffin, stearic acid, sodium acetate trihydrate and pentaglycerin) have been elaborated and characterized. The synthesis of all these measurements allowed us to select three composites whose characteristics match their integration into a solar thermal collector. [Copyright &y& Elsevier]

Abstract: Conventional phase change materials (PCMs) are already well known for their high thermal capacity and constant working temperature for thermal storage applications. Nevertheless, their low thermal conductivity (around 1Wm−1 K−1) leads to low and decreasing heat storage and discharge powers. Up to now, this major drawback has drastically inhibited their possible applications in industrial or domestic fields. The use of graphite to enhance the thermal conductivity of those materials has been already proposed in the case of paraffin but the corresponding applications are restricted to low-melting temperatures (below 150°C). For many applications, especially for solar concentrated technologies, this temperature range is too low. In the present paper, new composites made of salts or eutectics and graphite flakes, in a melting temperature range of 200–300°C are presented in terms of stability, storage capacity and thermal conductivity. The application of those materials to thermal storage is illustrated through simulated results according to different possible designs. The synergy between the storage composite properties and the interfacial area available for heat transfer with the working fluid is presented and discussed. [Copyright &y& Elsevier]

Abstract: Alternative low cost materials are evaluated through the valorization of by-products derived from mining and metallurgical industry for solid sensible heat based energy storage systems. They were used either as received or formulated as aggregates in mortars, and their thermal and mechanical properties were characterized. A selection methodology was applied in order to compare them with available materials found in the literature for applications as (STES) materials, and with materials from Cambridge Educational Software (CES) Selector database. It was demonstrated that these recycled materials have a high potential for these thermal energy storage applications. [Copyright &y& Elsevier]

Abstract: Hazardous wastes, such as asbestos-containing wastes (ACW) or fly ashes (FA) resulting from municipal solid waste incineration, can be converted into inert materials using plasma torch technology. Depending on the origin of the wastes and on the cooling conditions, the materials obtained at room temperature can be glassy or partially crystallized. The aim of this work is to investigate the potential valorisation of such inertized products as sensible heat material for high temperature thermal storage in thermodynamic solar power plants. Thermal stability and optical properties have been studied from room temperature up to 1000°C by infrared spectroscopy, differential scanning calorimetry and X-ray diffraction. All the studied materials are stable and present high total emissivity within the experimented temperature range. Their physical and chemical characteristics make of them to be good candidates for sensible heat storage materials. [Copyright &y& Elsevier]

Compatibility tests involving four vegetable oils and three different solid materials were performed, with a focus on rapeseed oil and quartzite rock. The objective was to verify the relevance of using vegetable oils as heat transfer fluid in concentrated solar power plants with direct thermocline thermal energy storage. First tests consisted in using small crucibles to put in contact rapeseed oil respectively with quartzite, blast furnace slags and alumina for 2160 h and at 210 °C. On a chemical point of view, the oil composition was modified by ageing and contact with solids. However, thermal properties that drive heat transfer (density, specific heat, thermal conductivity and dynamic viscosity) were not modified. Thermal stability temperature and flash point decreased and a correlation with the index of acidity of the samples has been found. Second set of tests consisted in putting in contact quartzite with rapeseed, palm, soybean and jatropha oils for 720 h and at 210 °C. Results confirmed that index of acidity can be a good indicator of the vegetable oil ageing. From the whole study, no incompatibility has been concluded, but one may recommend a limit value of 25 mg KOH.g−1 for the index of acidity to consider partial replacement of the vegetable heat transfer. • Compatibility tests involving several vegetables oils and solid materials. • Aging for more than 2000 h of tests performed at temperatures above to 200 °C. • Oils chemical composition and oils thermal properties evolutions. • Definition of a convenient indicator of vegetable oil aging. [ABSTRACT FROM AUTHOR]